The invention relates to apparatus and a method of continuously casting a steel strand having a length exceeding the length of a mould having a closed bottom. Into mould molten steel is introduced from a casting container or a tundish, and during the casting procedure the mould is moved away from the casting container or tundish along a substantially horizontal path so as to form a steel strand having a solidified strand skin and a liquid core. Further molden steel is poured from the casting container or tundish through the solidified strand skin in the direction to the mould bottom.
A method of this kind is disclosed in U.S. Pat. No. 3,517,725 and in the publication by H. E. Allen, L. Watts and R. Hadden, "Horizontal Continuous Casting in a Closed-End Mold System, The Watts Process", Continuous Casting, Biarritz, France, May 30th to June 2nd, 1976 (publication of lectures at a Continuous Casting Convention).
The disadvantage of the known method consists in that the longer the casting is continued, the smaller the channel for the supply of steel from the tundish to the continuous casting mould becomes, i.e. the diameter of the liquid core reduces over the entire length of the strand. Thereby the length of the strands is limited. It is a further disadvantage that the temperature sinks so low as a consequence of the heat emission from the strand surface to the environment by radiation or cooling, respectively, that it is below the liquidus temperature of the steel over a substantial part of the longitudinal extension. This condition arises at a short distance behind the outflow opening of the tundish. From this point to the bottom of the mould there is created a zone with a 2-phase mixture comprised of liquid melt and solidified crystals, which, when the procedure has been finished, is caused to solidify. The presence of this 2-phase-mixture over such a great length of the strand is a grave disadvantage since the mixture solid/liquid gradually becomes more semiliquid and the uniform supply of steel to the bottom of the mould is not safeguarded. Also, the uniform solidification and homogeneity of the cast strand is not safeguearded with this known method of operation.